Antennas are designed to project beams of a certain shape for both transmitting and receiving radio waves. For example, geo-stationary satellite mounted antennas may be configured to project a beam that is roughly the shape of a geographic region, such as a state within the United States. Thus, the satellite antenna is configured to transmit radio waves to and receive radio waves from the geographic region on the earth's surface defined by the beam.
From time to time it may be desirable to change the shape of the beam that a given antenna transmits and receives in. The change may be necessitated by a change in the geographic distribution of demand for a communications service provided via the antenna, by a need to transfer the satellite to a different orbital location, or by a need to respond to an emergency. When the antenna is mounted on a satellite, there is no economically feasible way to retrieve and reconfigure the antenna. Therefore, it would be desirable to provide dynamically configurable antennas that are capable of being reconfigured to form beams of different shapes from a remote location.
There are at least two conventional techniques for reconfiguring the shape of a beam produced by an antenna. In the first technique, an array of horns is configured to transmit/receive via a reflector. In the case of transmission, for example, by varying the amplitude and phase excitation of each horn in the array of horns, the beam shape may be changed to a desired shape.
In the second technique a single or multiple horns are configured to transmit and receive via a reflector. The reflector is either shaped or unshaped. In its unshaped configuration, the reflector is a paraboloid. In its shaped configuration, the reflector may be shaped to reflect radio waves to produce the desired shape. To make the antenna configurable, the reflector is made deformable and includes motors or servos coupled to its non-reflective side. The motors or servos may be commanded to urge the reflector into different shapes thus producing a corresponding change in shape of the transmitted and received beams.
Each of these conventional techniques has disadvantages. In the case of the array of horns, the array is heavy which may add substantially to launch costs in the case of a satellite based antenna. The array of horns also takes up a substantial amount of space compared to other antenna configurations, particularly where 100 or more horns are required for the array. Available space on a satellite for mounting apparati is scarce, particularly as a goal of satellite design is miniaturization. Therefore, this conventional technique may not be practical for many if not most satellite communication applications.
In the case of using motors or servos to urge a reflector into different shapes to produce a corresponding change in beam shape, this technique is clumsy. Moreover, it may be expensive, inaccurate, heavy by comparison to other antenna configurations and prone to failure.
It would be desirable to provide a new technique for remotely reconfiguring an antenna to form beams of different shapes. It would further be desirable for the new technique to be inexpensive, light weight and take up correspondingly less space on a satellite than conventional techniques.